fat mallet:
On vehicles carrying flammables leaving the lights on has something to do with the discharging of static electric,
Hi fat mallet, WELCOME 
Now Iāve heard that too, so unless youāve got something credible in writingā¦ Iām undecided.
It just might be a driverās myth.
fat mallet:
as static sparks are unseen but can be explosive in the right conditions
Thatās true mate, but only if a spark can jump to earth.
My dad used to be on the white oils many moons ago & IIRC there was an earting point on the motor somewhere, but static sparks are common on powder tanks, something to do with the method of discharge, I remember reading about it in āa day in the lifeā type story in one of the mags, dunno how it all works but nothing to do with headlights thatās for sure 
newmercman:
My dad used to be on the white oils many moons ago & IIRC there was an earting point on the motor somewhere, but static sparks are common on powder tanks, something to do with the method of discharge, I remember reading about it in āa day in the lifeā type story in one of the mags, dunno how it all works but nothing to do with headlights thatās for sure
Hi newmercman, Iād say youāre spot-on mate.
Tankers carrying flammables (liquid or solid) need to earth between the tanker and the installation that theyāre delivering to, or loading from. Thatās to get rid of the electrical difference between the two lumps of metal.
The same applies to many powder tanks too, because powders can form a combustible atmosphere even if the stuff isnāt flammable in the accepted sense, eg. flour.
Static electricity is caused whenever two non-conductive substances rub against each other, eg. when a liquid or powdery or granular substance is squirted through a pipe, or when a platic comb is used to comb dry hair. If the tanker is earthed to the installation, then the static has an escape route and wonāt collect and wait for somewhere to jump to. The static electricity would otherwise collect on the tanker, due to the tanker being insulated from earth by its rubber tyres. In that case, the static has nowhere to go.
Thatās why we sometimes get a static shock when we reach for our car door. Shocking.